return 404 with vod module

docker/main/rootfs/usr/local/nginx/conf/nginx.conf

@@ -109,6 +109,14 @@ http {
             expires off;
 
             keepalive_disable safari;
+
+            # vod module returns 502 for non-existent media
+            # https://github.com/kaltura/nginx-vod-module/issues/468
+            error_page 502 =404 /vod-not-found;
+        }
+
+        location = /vod-not-found {
+            return 404;
         }
 
         location /stream/ {